This invention relates to a sand blasting abrasive material, a sand blasting method for a wafer using the same and a wafer processed by means of the sand blasting method.
There has been employed a gettering technique in a semiconductor device fabrication process by which contaminating impurities mainly including heavy metals are collected to strained sites produced outside element forming regions of a wafer in a element forming step, as means suppressing generation of crystal defects to be otherwise caused by contaminating materials on element forming surfaces of the regions.
A sand blasting method has been available as the easiest means for gettering. This method is such that a sand blasting abrasive material in the form of fine particulate is blown mainly against a rear surface opposite from an element forming surface of a wafer to create mechanically induced strain in the wafer. As the sand blasting method, two methods are adopted: one, in which natural quartz powder, synthetic quartz powder or the like powder is blown against a wafer in a powdery state without any modification thereon (a dry method) and the other, in which such powder is blown against a wafer in the form of slurry as a mixture with pure water (a wet method). It should be appreciated that as abrasive material, natural quartz powder can be used advantageously over synthetic quartz powder in that a necessary OSF (Oxidation Induced Stacking Fault) density cannot be obtained with synthetic quartz powder and in addition the synthetic quartz powder is more expensive.
As described above, while natural quartz powder is advantageous in terms of cost and so on, metal ions such as Fe ion, Ni ion, Cu ion, Zu ion, Al ion and so on, though in only trace amounts, are included therein. When a slurry is prepared adding pure water to natural quartz powder containing such metal ions, Cu ion has a low ionization tendency and is easy to deposit on a wafer surface. Further, Cu shows a high diffusion coefficient in a typical semiconductor material Si and therefore intrudes into the interior of a Si with ease, contributing very unfavorably to the Si wafer in terms of metal contamination.
When metal contamination arises, various kinds of crystal defects are induced in heat treatments of a wafer in a device fabrication process by the above described metal impurities in the bulk of the wafer. The crystal defects are also generated on a surface and in the vicinity thereof and therefore, a leakage current increases in device chips obtained from the wafer, thereby not only deteriorating device characteristics but reducing a device yield.
The invention has been made in light of such problems and it is accordingly an object of the invention to provide a sand blasting abrasive material and a sand blasting method for a wafer using the same, which prevents contamination of the wafer by a metal ion from occurring.
A sand blasting abrasive material of the invention for achieving the above object contains a chelating agent.
The chelating agent is preferably selected from the group consisting of the following compounds (1) to (4) and salts thereof:
(1) Nitrilotriacetic acid (NTA)
(2) Ethylenediaminetetraacetic acid (EDTA)
(3) Diethylenediamine-N,N,Nxe2x80x3,Nxe2x80x3-pentaacetic acid (DTPA)
(4) Cyclohexanediaminetetraacetic acid (CyDTA)
A molar concentration of a chelating agent described above is preferably 4.28xc3x9710xe2x88x924 mol/l or more and more preferably 2.57xc3x9710xe2x88x923 mol/l or more.
Further, a sand blasting abrasive material of the invention is preferably composed of natural quartz powder as a major component and also preferably a slurry prepared by adding natural quartz powder into pure water.
A wafer of the invention is one processed with the above described sand blasting abrasive material.
A sand blasting method for a wafer of the invention is to sand blast a wafer with the above described sand blasting abrasive material.